1. Field of the Invention
The present invention relates to a method of controlling torque and an apparatus using the same, and more particularly, a method of controlling torque and an apparatus using the same, which control the output torque under the predetermined working and control conditions, according to a correspondence between the air pressure and the torque constructed in advance.
2. Description of the Related Art
For all the torque tools driven by compressed air, such as pneumatic impact wrenches, pneumatic oil pulse wrenches, pneumatic torque multipliers, pneumatic screwdrivers with clutch, and so on, their test results or operating performance tend to be affected by an unstable working air pressure during the process of testing or operating them. Conventional pneumatic torque tools usually have their torque controlled by the pressure or airflow of the compressed air driving those tools. Since the compressed air driving the pneumatic torque tools is affected by the factors such as the capability of the on-site compressed air system to supply gas, the torque driving structure of the tools, and the air consumptions of the tools, it is hard to control the magnitudes of their output torques.
The output torque of the conventional impact torque tool is usually controlled by adjusting the air supply pressure and the airflow thereof, or by adjusting the pressure, the airflow and the duration of fastening operation. However, since the working air pressure during the fastening operation is not stable, the airflow to the tool is directly affected, which in turn causes the deviation of the output torque to be extremely large. Even if the tool is disposed with a torque measuring device, the frequency and amplitude of the vibration that arises from the impact will pose difficulty for the analysis of signals, and hence it will be difficult to control the torque output effectively.
The output torque of conventional oil pulse torque tools is normally controlled by adjusting their working air pressure and the oil pressure in the hydraulic cylinder. Despite having a better torque control precision compared to the former, numerous factors, such as the unstable air pressure during the fastening process directly affecting the airflow to the tool, or the structural feature of the hydraulic cylinder and the rising temperature of the hydraulic fluid inside the cylinder during continuous operation, tend to limit the range of adjustment and the control precision of the torque.
The static torque tool achieves torque amplification through the pneumatic motor coupled with structures such as the planetary gearing and reaction arm. The precision thereof is higher albeit the time it takes to fasten is longer, and the slow speed results in low efficiency, not to mention the tool is heavier, which tends to cause fatigue in the operator.
A torque tool with clutch is a tool that achieves torque control via a pneumatic motor working in conjunction with the planetary reduction gearing, in addition to the tension of a spring pushing against the clutch; while it has an acceptable control precision, nevertheless, when the operation of the tool is halted, the reaction force generated increases as the torque output of the tool increases, thereby making it difficult to handle the tool for a prolonged period of time, or even causing issues such as fatigue or occupational injury such as elbow arthritis to the operation personnel. As a consequence, the industry has been working on combining the advantages of those tools mentioned above with various torque measuring and control devices to improve the precision of output torque control.
There are numerous means and methods to control the torque of a torque tool, usually their torque is controlled through the use of torque measuring device utilizing pressure (air pressure or oil pressure), flow rate (air consumption of the tool), the deformation and angle of the torque output shaft, or the electromagnetic induction coil, or through the use of torque control device incorporating the spring tension and clutch, or even the duration of fastening. Their results, however, are quite limited.
In conclusion, the majority of torque tools control the torque by means of deformation signals detected by the deformation sensor (e.g. strain gauge or solenoid electromagnetic induction coil), which is installed at suitable positions such as the output shaft of those tools, or by calculating the angular displacement (e.g. using a gyroscope) after the surfaces of the bolt and the fastened object come into contact, in conjunction with the calculation of the fastening duration, or the flow rate or the pressure of air entering the driving motor of the tools. However, since the pulse signals generated by the impacts of the impact or oil pulse torque tools are erratic and the fastening duration thereof is too short, it is hard to control the torque of such tools. In addition, when the detected signals, which are generated by those electronic detection apparatus installed in the tools, is to be transmitted to the built-in or external control apparatus of the tool, so as to shut off the air supply in real-time, the accuracy of the torque control is bound to be affected because of the hysteresis of the signal transmission when the signals are being relayed between electronic and the mechanical components, such as between the microprocessor and the solenoid valve; moreover, the conditions of the fastener and the object to be fastened, e.g. the material, surface smoothness, hardness or surface lubrication, or even the way the operator holding the tool while fastening, will directly or indirectly affect the accuracy of the torque control.
To this end, the inventor of the present invention has spent countless years researching in torque control products, and has managed to obtain the patents as follows: “Anti-vibration torque sensing and control device for tools” (US Publication No. U.S. Pat. No. 7,779,704), “Apparatus capable of controlling, tracking and measuring tightening torque and locking force, and method for controlling, tracking, measuring and calibrating thereof” (China Publication No. ZL 201210011877.1), “Torque control apparatus of dynamic locking tool and its control procedure” (Taiwan Publication No. 1396609), and “Torque control device for an impact type pneumatic torsion spanner” (Taiwan Publication No. 1432293); the inventor subsequently delves further into the operating characteristics of the impact or oil pulse torque tool, and with the confirmation from various empirical data, the inventor develops a method of controlling torque and an apparatus using the same, in order to solve the most challenging problem, i.e. the control and measurement of the torque of pneumatic impact or pulse torque wrench, which has been troubling the industry for years, thereby remedying the shortcomings in the state of the art and promoting the practicality of the tool in the industry.